Linear motors are well known devices, in which one of a coil or a magnet element is mounted to a fixed member and the other element to a member to be moved. An electric current is applied to the coil, which generates magnetic lines of force to interact with the magnet to produce linear motion of the movable member. Such linear motors are generally used in refrigeration compressors, in which the movable member is defined by the piston of the compressor, and the magnet is mounted to said piston. The coil is fixedly mounted to an external portion of the compressor structure that forms the cylinder within which the piston is reciprocated.
In a linear compressor of one known type, such as shown in FIG. 1, the compression of the gas results from the axial movement of a piston 1 inside a cylinder 2 that has an external block 2a with a vertical wall 2b. The cylinder is closed by a cylinder head 3 on which is mounted a valve plate 3d on which are positioned a suction valve 3a and a discharge valve 3b. The suction and discharge valves regulate the inlet and outlet of the gas compressed in the cylinder 2. All of these elements are provided within a hermetic shell 8, which typically is of cylindrical shape. There is an inlet conduit 31 forming a passage through the shell 8 for the low pressure gas directed to the suction valve 3a, and an outlet conduit 32 forming a passage through the shell 8 for the compressed gas coming from the discharge valve 3b and which is directed to the outside of the shell 8.
The piston 1 is driven by a linear electric motor formed by a ring shaped actuator 4 that is attached to a base flange 1a of the piston 1. The upper end of the actuator 4 supports a magnet member 5, of toroidal shape and usually formed of a plurality of permanent magnets. A coil 6 of toroidal shape and made of wire is fixedly mounted to the inner lamination 6a of a lamination stack of the stator of the linear motor. Electrical current is supplied to the coil 6 to produce magnetic lines of force to interact with the magnet member 5 and produce linear reciprocating motion of the actuator 4 and the piston 1, with the magnet member 5 moving between the coil 6 and an external lamination 6b of the lamination stack of the stator of the linear motor.
The piston 1 has its base flange 1a incorporating an axial projection 1b connected to the center of a set of flat springs 7, and the edges of the set of springs 7 are rigidly mounted by suitable connectors 10 to the vertical wall 2b of the cylinder. The flat springs 7 are made of sheet steel and move up and down as the piston 1 moves in a linear reciprocation as driven by the linear motor.
The piston 1, the actuator 4, the magnet member 5 and the set of flat springs 7 form together a resonant, or movable, assembly of the compressor. That is, said assembly moves relative to the cylinder 2. The cylinder 2, the cylinder block 2a and the elements affixed to it, such as the head 3, are stationary. These elements are hereafter referred to as the reference, or stationary, assembly.
The elements of the reference assembly carry the elements of the resonant assembly, so that the compressor can be mounted to the shell. As illustrated, all of the operating elements of the compressor are mounted to the bottom wall of the shell 8 by a plurality of resilient suspension elements, shown in the form of springs 9 of the helical type. There can be as many of the springs 9 as needed and these are adequately dimensioned in relation to the weight, or mass, of the various compressor elements and the forces that these elements generate. The springs 9 may be of any suitable shape to absorb the forces as the compressor operates with the piston reciprocating. As can be seen in the compressor shown in FIG. 1, all of the forces produced during operation are largely transmitted to one end of the shell to which the springs 9 are mounted.
FIG. 2 is a schematic diagram of the elements of the compressor of FIG. 1. The elements are designated by:    Ma=mass of the resonant assembly (elements 1, 4, 5, 7)    Mb=mass of the reference assembly (elements 2, 2a, 2b, 3)    Kr=spring constant of the set of flat springs (7) of the resonant assembly    Ks=spring constant of the set of suspension springs (9)
In the compressor of FIG. 1, the suspension springs 9 that mount the complete assembly of compressor elements to the shell 8 have the spring constant Ks. The function of the suspension springs 9 is to minimize the transmission of vibration from the compressor itself (the moving piston acting as a compression pump) to the hermetic shell 8. The spring constant Kr of the set of springs 7 is related to the compression ratio of the compressor. The spring constant Ks of the set of suspension springs 9 usually is many times smaller than that of the spring constant Kr of the set of flat springs 7, in order to have no influence in the mechanical resonance frequency of the masses Ma and Mb of the compressor elements.
During operation of the compressor, the assembly of resonant elements having the mass Ma is displaced by the linear motor in relation to the assembly of reference elements having mass Mb. Due to the principle of action/reaction, the reference assembly will have a displacement on the set of suspension springs 9 that is proportional to the ratio of the masses Ma and Mb of the resonant and reference assemblies. The displacement of the reference assembly, supported by the suspension springs 9, transmits a force to the shell 8 of the compressor as the resonant assembly reciprocates, causing the shell 8 to vibrate. Such vibration is undesirable for this type of compressor, especially when used in residential refrigeration systems. Accordingly, it would be desirable to provide a mounting arrangement for such a linear compressor that reduces the amount of vibration and which is simple and inexpensive in construction and assembly.